In many cases, an artificial ventilation is necessary in the treatment of a patient, for example, in the area of intensive care, in surgeries or in emergency situations. Depending on the application in this case, external devices take over the respiration of a patient entirely or assist it. Thus, for example, respirators without rebreathing are used for the artificial ventilation of patients on intensive care units in hospital, while in anesthesia devices with closed system, the exhalation gas exhaled by the patient is reused as inhalation gas. The technical solution described in detail below for generating an alarm can be used both for correspondingly designed ventilators (also known as respirators) and for anesthesia devices.
Avoiding clinically irrelevant alarms has great importance in today's medical devices. While for a long time the focus in the development of alarm-capable monitoring devices was placed on the clear and early recognition and alerting of dangerous situations in the monitoring of a patient, nowadays reduction in the number of alarms to a clinically necessary minimum is more and more the focus. This can, above all, be attributed to the fact that more and more alarm-capable devices, for example, syringe pumps, monitors and respirators, are arranged in the area of the patient. Thus, the health care staff as well as the patients are exposed to a high acoustic discomfort and the risks resulting from this are among the highest that are currently connected with medical devices. Based on the problem described, nowadays a principal aspect in the development of medical devices subject to alarm lies in optimizing the alarm frequency to the effect that, on the one hand, dangerous situations are always clearly recognized and, on the other hand, irrelevant alarms are largely suppressed. In this way, an insidious desensitization of the health care staff because of the many alarms shall be prevented in spite of maintaining a high safety standard.
A process for alarm generation in alarm-capable medical devices is known from EP 2 302 606 B1. The process described is essentially based on the fact that, in addition to establishing relevant limit values, a so-called verification interval is recorded, whereby an alarm is only triggered if a preset limit value is undershot or overshot over the entire duration of the verification interval. In each case, the recorded verification interval has a time-limited verification interval length, which usually decreases with increasing degree of danger of the patient. The delay interval length defined for the lowest degree of danger thus corresponds to the maximum possible alarm delay of a slight over- or undershooting of the corresponding limit value, while an alarm is very quickly triggered in case of sharp deviations of a recorded measured value from the limit value. The establishing of a danger potential is thus essential to the technical solution described.
In order to be able to optimally estimate possible dangerous situations in an artificial ventilation of a patient, it is necessary to consider additional characteristics, for example, a breathing disorder that is present during the monitoring of the patient's parameters. In case of monitoring limits that are set too closely, this frequently leads to alarms regardless of whether a danger to the patient is present. However, a general weakening of the alarm limits is also not a suitable means for minimizing the alarm frequency here, since this would lead to a lower sensitivity of the monitoring. Provided that there is no contraindication and the remaining monitored parameters, for example, oxygen saturation or CO2 partial pressure, during the monitoring of the breathing activity, lie within an acceptable range, a triggering of an alarm is dispensable in case of an at least only short-term over- or undershooting of the limit values. It follows from this that provided that no worsening of the state of the patient overall is recognized, an alarm-free toleration of a pathological breathing pattern rated as acceptable with regard to the patient's risk is permissible.
The minute volume represents an important parameter in the monitoring of the artificial ventilation of a patient. This value, which is used as a standard in medicine, for the air volume provided to the lung within one minute provides important evidence of the oxygenation and ventilation of a patient and is therefore an obligatory measured quantity for the monitoring of a patient in intensive care. In case of an exclusively mandatory ventilation of a patient, the minute volume corresponds to the product of the applied tidal volume and the respiratory rate.
However, no devices are currently known from the state of the art that analyze information about a concretely present breathing disorder. Hence, a distinction cannot be made between a supposed and an actual danger to the patient. Furthermore, the input possibilities for the alarm limits are limited and are oriented towards the technical monitoring of measured values instead of a patient-centered monitoring.